/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 *
 */

package java.io;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.security.AccessController;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import sun.misc.Unsafe;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.reflect.ReflectionFactory;
import sun.reflect.misc.ReflectUtil;

/**
 * Serialization's descriptor for classes.  It contains the name and
 * serialVersionUID of the class.  The ObjectStreamClass for a specific class
 * loaded in this Java VM can be found/created using the lookup method.
 *
 * <p>The algorithm to compute the SerialVersionUID is described in
 * <a href="../../../platform/serialization/spec/class.html#4100">Object
 * Serialization Specification, Section 4.6, Stream Unique Identifiers</a>.
 *
 * @author Mike Warres
 * @author Roger Riggs
 * @see ObjectStreamField
 * @see <a href="../../../platform/serialization/spec/class.html">Object Serialization
 * Specification, Section 4, Class Descriptors</a>
 * @since JDK1.1
 */
public class ObjectStreamClass implements Serializable {

  /**
   * serialPersistentFields value indicating no serializable fields
   */
  public static final ObjectStreamField[] NO_FIELDS =
      new ObjectStreamField[0];

  private static final long serialVersionUID = -6120832682080437368L;
  private static final ObjectStreamField[] serialPersistentFields =
      NO_FIELDS;

  /**
   * reflection factory for obtaining serialization constructors
   */
  private static final ReflectionFactory reflFactory =
      AccessController.doPrivileged(
          new ReflectionFactory.GetReflectionFactoryAction());

  private static class Caches {

    /**
     * cache mapping local classes -> descriptors
     */
    static final ConcurrentMap<WeakClassKey, Reference<?>> localDescs =
        new ConcurrentHashMap<>();

    /**
     * cache mapping field group/local desc pairs -> field reflectors
     */
    static final ConcurrentMap<FieldReflectorKey, Reference<?>> reflectors =
        new ConcurrentHashMap<>();

    /**
     * queue for WeakReferences to local classes
     */
    private static final ReferenceQueue<Class<?>> localDescsQueue =
        new ReferenceQueue<>();
    /**
     * queue for WeakReferences to field reflectors keys
     */
    private static final ReferenceQueue<Class<?>> reflectorsQueue =
        new ReferenceQueue<>();
  }

  /**
   * class associated with this descriptor (if any)
   */
  private Class<?> cl;
  /**
   * name of class represented by this descriptor
   */
  private String name;
  /**
   * serialVersionUID of represented class (null if not computed yet)
   */
  private volatile Long suid;

  /**
   * true if represents dynamic proxy class
   */
  private boolean isProxy;
  /**
   * true if represents enum type
   */
  private boolean isEnum;
  /**
   * true if represented class implements Serializable
   */
  private boolean serializable;
  /**
   * true if represented class implements Externalizable
   */
  private boolean externalizable;
  /**
   * true if desc has data written by class-defined writeObject method
   */
  private boolean hasWriteObjectData;
  /**
   * true if desc has externalizable data written in block data format; this
   * must be true by default to accommodate ObjectInputStream subclasses which
   * override readClassDescriptor() to return class descriptors obtained from
   * ObjectStreamClass.lookup() (see 4461737)
   */
  private boolean hasBlockExternalData = true;

  /**
   * Contains information about InvalidClassException instances to be thrown
   * when attempting operations on an invalid class. Note that instances of
   * this class are immutable and are potentially shared among
   * ObjectStreamClass instances.
   */
  private static class ExceptionInfo {

    private final String className;
    private final String message;

    ExceptionInfo(String cn, String msg) {
      className = cn;
      message = msg;
    }

    /**
     * Returns (does not throw) an InvalidClassException instance created
     * from the information in this object, suitable for being thrown by
     * the caller.
     */
    InvalidClassException newInvalidClassException() {
      return new InvalidClassException(className, message);
    }
  }

  /**
   * exception (if any) thrown while attempting to resolve class
   */
  private ClassNotFoundException resolveEx;
  /**
   * exception (if any) to throw if non-enum deserialization attempted
   */
  private ExceptionInfo deserializeEx;
  /**
   * exception (if any) to throw if non-enum serialization attempted
   */
  private ExceptionInfo serializeEx;
  /**
   * exception (if any) to throw if default serialization attempted
   */
  private ExceptionInfo defaultSerializeEx;

  /**
   * serializable fields
   */
  private ObjectStreamField[] fields;
  /**
   * aggregate marshalled size of primitive fields
   */
  private int primDataSize;
  /**
   * number of non-primitive fields
   */
  private int numObjFields;
  /**
   * reflector for setting/getting serializable field values
   */
  private FieldReflector fieldRefl;
  /**
   * data layout of serialized objects described by this class desc
   */
  private volatile ClassDataSlot[] dataLayout;

  /**
   * serialization-appropriate constructor, or null if none
   */
  private Constructor<?> cons;
  /**
   * class-defined writeObject method, or null if none
   */
  private Method writeObjectMethod;
  /**
   * class-defined readObject method, or null if none
   */
  private Method readObjectMethod;
  /**
   * class-defined readObjectNoData method, or null if none
   */
  private Method readObjectNoDataMethod;
  /**
   * class-defined writeReplace method, or null if none
   */
  private Method writeReplaceMethod;
  /**
   * class-defined readResolve method, or null if none
   */
  private Method readResolveMethod;

  /**
   * local class descriptor for represented class (may point to self)
   */
  private ObjectStreamClass localDesc;
  /**
   * superclass descriptor appearing in stream
   */
  private ObjectStreamClass superDesc;

  /**
   * Initializes native code.
   */
  private static native void initNative();

  static {
    initNative();
  }

  /**
   * Find the descriptor for a class that can be serialized.  Creates an
   * ObjectStreamClass instance if one does not exist yet for class. Null is
   * returned if the specified class does not implement java.io.Serializable
   * or java.io.Externalizable.
   *
   * @param cl class for which to get the descriptor
   * @return the class descriptor for the specified class
   */
  public static ObjectStreamClass lookup(Class<?> cl) {
    return lookup(cl, false);
  }

  /**
   * Returns the descriptor for any class, regardless of whether it
   * implements {@link Serializable}.
   *
   * @param cl class for which to get the descriptor
   * @return the class descriptor for the specified class
   * @since 1.6
   */
  public static ObjectStreamClass lookupAny(Class<?> cl) {
    return lookup(cl, true);
  }

  /**
   * Returns the name of the class described by this descriptor.
   * This method returns the name of the class in the format that
   * is used by the {@link Class#getName} method.
   *
   * @return a string representing the name of the class
   */
  public String getName() {
    return name;
  }

  /**
   * Return the serialVersionUID for this class.  The serialVersionUID
   * defines a set of classes all with the same name that have evolved from a
   * common root class and agree to be serialized and deserialized using a
   * common format.  NonSerializable classes have a serialVersionUID of 0L.
   *
   * @return the SUID of the class described by this descriptor
   */
  public long getSerialVersionUID() {
    // REMIND: synchronize instead of relying on volatile?
    if (suid == null) {
      suid = AccessController.doPrivileged(
          new PrivilegedAction<Long>() {
            public Long run() {
              return computeDefaultSUID(cl);
            }
          }
      );
    }
    return suid.longValue();
  }

  /**
   * Return the class in the local VM that this version is mapped to.  Null
   * is returned if there is no corresponding local class.
   *
   * @return the <code>Class</code> instance that this descriptor represents
   */
  @CallerSensitive
  public Class<?> forClass() {
    if (cl == null) {
      return null;
    }
    if (System.getSecurityManager() != null) {
      Class<?> caller = Reflection.getCallerClass();
      if (ReflectUtil.needsPackageAccessCheck(caller.getClassLoader(), cl.getClassLoader())) {
        ReflectUtil.checkPackageAccess(cl);
      }
    }
    return cl;
  }

  /**
   * Return an array of the fields of this serializable class.
   *
   * @return an array containing an element for each persistent field of this class. Returns an
   * array of length zero if there are no fields.
   * @since 1.2
   */
  public ObjectStreamField[] getFields() {
    return getFields(true);
  }

  /**
   * Get the field of this class by name.
   *
   * @param name the name of the data field to look for
   * @return The ObjectStreamField object of the named field or null if there is no such named
   * field.
   */
  public ObjectStreamField getField(String name) {
    return getField(name, null);
  }

  /**
   * Return a string describing this ObjectStreamClass.
   */
  public String toString() {
    return name + ": static final long serialVersionUID = " +
        getSerialVersionUID() + "L;";
  }

  /**
   * Looks up and returns class descriptor for given class, or null if class
   * is non-serializable and "all" is set to false.
   *
   * @param cl class to look up
   * @param all if true, return descriptors for all classes; if false, only return descriptors for
   * serializable classes
   */
  static ObjectStreamClass lookup(Class<?> cl, boolean all) {
    if (!(all || Serializable.class.isAssignableFrom(cl))) {
      return null;
    }
    processQueue(Caches.localDescsQueue, Caches.localDescs);
    WeakClassKey key = new WeakClassKey(cl, Caches.localDescsQueue);
    Reference<?> ref = Caches.localDescs.get(key);
    Object entry = null;
    if (ref != null) {
      entry = ref.get();
    }
    EntryFuture future = null;
    if (entry == null) {
      EntryFuture newEntry = new EntryFuture();
      Reference<?> newRef = new SoftReference<>(newEntry);
      do {
        if (ref != null) {
          Caches.localDescs.remove(key, ref);
        }
        ref = Caches.localDescs.putIfAbsent(key, newRef);
        if (ref != null) {
          entry = ref.get();
        }
      } while (ref != null && entry == null);
      if (entry == null) {
        future = newEntry;
      }
    }

    if (entry instanceof ObjectStreamClass) {  // check common case first
      return (ObjectStreamClass) entry;
    }
    if (entry instanceof EntryFuture) {
      future = (EntryFuture) entry;
      if (future.getOwner() == Thread.currentThread()) {
                /*
                 * Handle nested call situation described by 4803747: waiting
                 * for future value to be set by a lookup() call further up the
                 * stack will result in deadlock, so calculate and set the
                 * future value here instead.
                 */
        entry = null;
      } else {
        entry = future.get();
      }
    }
    if (entry == null) {
      try {
        entry = new ObjectStreamClass(cl);
      } catch (Throwable th) {
        entry = th;
      }
      if (future.set(entry)) {
        Caches.localDescs.put(key, new SoftReference<Object>(entry));
      } else {
        // nested lookup call already set future
        entry = future.get();
      }
    }

    if (entry instanceof ObjectStreamClass) {
      return (ObjectStreamClass) entry;
    } else if (entry instanceof RuntimeException) {
      throw (RuntimeException) entry;
    } else if (entry instanceof Error) {
      throw (Error) entry;
    } else {
      throw new InternalError("unexpected entry: " + entry);
    }
  }

  /**
   * Placeholder used in class descriptor and field reflector lookup tables
   * for an entry in the process of being initialized.  (Internal) callers
   * which receive an EntryFuture belonging to another thread as the result
   * of a lookup should call the get() method of the EntryFuture; this will
   * return the actual entry once it is ready for use and has been set().  To
   * conserve objects, EntryFutures synchronize on themselves.
   */
  private static class EntryFuture {

    private static final Object unset = new Object();
    private final Thread owner = Thread.currentThread();
    private Object entry = unset;

    /**
     * Attempts to set the value contained by this EntryFuture.  If the
     * EntryFuture's value has not been set already, then the value is
     * saved, any callers blocked in the get() method are notified, and
     * true is returned.  If the value has already been set, then no saving
     * or notification occurs, and false is returned.
     */
    synchronized boolean set(Object entry) {
      if (this.entry != unset) {
        return false;
      }
      this.entry = entry;
      notifyAll();
      return true;
    }

    /**
     * Returns the value contained by this EntryFuture, blocking if
     * necessary until a value is set.
     */
    synchronized Object get() {
      boolean interrupted = false;
      while (entry == unset) {
        try {
          wait();
        } catch (InterruptedException ex) {
          interrupted = true;
        }
      }
      if (interrupted) {
        AccessController.doPrivileged(
            new PrivilegedAction<Void>() {
              public Void run() {
                Thread.currentThread().interrupt();
                return null;
              }
            }
        );
      }
      return entry;
    }

    /**
     * Returns the thread that created this EntryFuture.
     */
    Thread getOwner() {
      return owner;
    }
  }

  /**
   * Creates local class descriptor representing given class.
   */
  private ObjectStreamClass(final Class<?> cl) {
    this.cl = cl;
    name = cl.getName();
    isProxy = Proxy.isProxyClass(cl);
    isEnum = Enum.class.isAssignableFrom(cl);
    serializable = Serializable.class.isAssignableFrom(cl);
    externalizable = Externalizable.class.isAssignableFrom(cl);

    Class<?> superCl = cl.getSuperclass();
    superDesc = (superCl != null) ? lookup(superCl, false) : null;
    localDesc = this;

    if (serializable) {
      AccessController.doPrivileged(new PrivilegedAction<Void>() {
        public Void run() {
          if (isEnum) {
            suid = Long.valueOf(0);
            fields = NO_FIELDS;
            return null;
          }
          if (cl.isArray()) {
            fields = NO_FIELDS;
            return null;
          }

          suid = getDeclaredSUID(cl);
          try {
            fields = getSerialFields(cl);
            computeFieldOffsets();
          } catch (InvalidClassException e) {
            serializeEx = deserializeEx =
                new ExceptionInfo(e.classname, e.getMessage());
            fields = NO_FIELDS;
          }

          if (externalizable) {
            cons = getExternalizableConstructor(cl);
          } else {
            cons = getSerializableConstructor(cl);
            writeObjectMethod = getPrivateMethod(cl, "writeObject",
                new Class<?>[]{ObjectOutputStream.class},
                Void.TYPE);
            readObjectMethod = getPrivateMethod(cl, "readObject",
                new Class<?>[]{ObjectInputStream.class},
                Void.TYPE);
            readObjectNoDataMethod = getPrivateMethod(
                cl, "readObjectNoData", null, Void.TYPE);
            hasWriteObjectData = (writeObjectMethod != null);
          }
          writeReplaceMethod = getInheritableMethod(
              cl, "writeReplace", null, Object.class);
          readResolveMethod = getInheritableMethod(
              cl, "readResolve", null, Object.class);
          return null;
        }
      });
    } else {
      suid = Long.valueOf(0);
      fields = NO_FIELDS;
    }

    try {
      fieldRefl = getReflector(fields, this);
    } catch (InvalidClassException ex) {
      // field mismatches impossible when matching local fields vs. self
      throw new InternalError(ex);
    }

    if (deserializeEx == null) {
      if (isEnum) {
        deserializeEx = new ExceptionInfo(name, "enum type");
      } else if (cons == null) {
        deserializeEx = new ExceptionInfo(name, "no valid constructor");
      }
    }
    for (int i = 0; i < fields.length; i++) {
      if (fields[i].getField() == null) {
        defaultSerializeEx = new ExceptionInfo(
            name, "unmatched serializable field(s) declared");
      }
    }
  }

  /**
   * Creates blank class descriptor which should be initialized via a
   * subsequent call to initProxy(), initNonProxy() or readNonProxy().
   */
  ObjectStreamClass() {
  }

  /**
   * Initializes class descriptor representing a proxy class.
   */
  void initProxy(Class<?> cl,
      ClassNotFoundException resolveEx,
      ObjectStreamClass superDesc)
      throws InvalidClassException {
    this.cl = cl;
    this.resolveEx = resolveEx;
    this.superDesc = superDesc;
    isProxy = true;
    serializable = true;
    suid = Long.valueOf(0);
    fields = NO_FIELDS;

    if (cl != null) {
      localDesc = lookup(cl, true);
      if (!localDesc.isProxy) {
        throw new InvalidClassException(
            "cannot bind proxy descriptor to a non-proxy class");
      }
      name = localDesc.name;
      externalizable = localDesc.externalizable;
      cons = localDesc.cons;
      writeReplaceMethod = localDesc.writeReplaceMethod;
      readResolveMethod = localDesc.readResolveMethod;
      deserializeEx = localDesc.deserializeEx;
    }
    fieldRefl = getReflector(fields, localDesc);
  }

  /**
   * Initializes class descriptor representing a non-proxy class.
   */
  void initNonProxy(ObjectStreamClass model,
      Class<?> cl,
      ClassNotFoundException resolveEx,
      ObjectStreamClass superDesc)
      throws InvalidClassException {
    this.cl = cl;
    this.resolveEx = resolveEx;
    this.superDesc = superDesc;
    name = model.name;
    suid = Long.valueOf(model.getSerialVersionUID());
    isProxy = false;
    isEnum = model.isEnum;
    serializable = model.serializable;
    externalizable = model.externalizable;
    hasBlockExternalData = model.hasBlockExternalData;
    hasWriteObjectData = model.hasWriteObjectData;
    fields = model.fields;
    primDataSize = model.primDataSize;
    numObjFields = model.numObjFields;

    if (cl != null) {
      localDesc = lookup(cl, true);
      if (localDesc.isProxy) {
        throw new InvalidClassException(
            "cannot bind non-proxy descriptor to a proxy class");
      }
      if (isEnum != localDesc.isEnum) {
        throw new InvalidClassException(isEnum ?
            "cannot bind enum descriptor to a non-enum class" :
            "cannot bind non-enum descriptor to an enum class");
      }

      if (serializable == localDesc.serializable &&
          !cl.isArray() &&
          suid.longValue() != localDesc.getSerialVersionUID()) {
        throw new InvalidClassException(localDesc.name,
            "local class incompatible: " +
                "stream classdesc serialVersionUID = " + suid +
                ", local class serialVersionUID = " +
                localDesc.getSerialVersionUID());
      }

      if (!classNamesEqual(name, localDesc.name)) {
        throw new InvalidClassException(localDesc.name,
            "local class name incompatible with stream class " +
                "name \"" + name + "\"");
      }

      if (!isEnum) {
        if ((serializable == localDesc.serializable) &&
            (externalizable != localDesc.externalizable)) {
          throw new InvalidClassException(localDesc.name,
              "Serializable incompatible with Externalizable");
        }

        if ((serializable != localDesc.serializable) ||
            (externalizable != localDesc.externalizable) ||
            !(serializable || externalizable)) {
          deserializeEx = new ExceptionInfo(
              localDesc.name, "class invalid for deserialization");
        }
      }

      cons = localDesc.cons;
      writeObjectMethod = localDesc.writeObjectMethod;
      readObjectMethod = localDesc.readObjectMethod;
      readObjectNoDataMethod = localDesc.readObjectNoDataMethod;
      writeReplaceMethod = localDesc.writeReplaceMethod;
      readResolveMethod = localDesc.readResolveMethod;
      if (deserializeEx == null) {
        deserializeEx = localDesc.deserializeEx;
      }
    }
    fieldRefl = getReflector(fields, localDesc);
    // reassign to matched fields so as to reflect local unshared settings
    fields = fieldRefl.getFields();
  }

  /**
   * Reads non-proxy class descriptor information from given input stream.
   * The resulting class descriptor is not fully functional; it can only be
   * used as input to the ObjectInputStream.resolveClass() and
   * ObjectStreamClass.initNonProxy() methods.
   */
  void readNonProxy(ObjectInputStream in)
      throws IOException, ClassNotFoundException {
    name = in.readUTF();
    suid = Long.valueOf(in.readLong());
    isProxy = false;

    byte flags = in.readByte();
    hasWriteObjectData =
        ((flags & ObjectStreamConstants.SC_WRITE_METHOD) != 0);
    hasBlockExternalData =
        ((flags & ObjectStreamConstants.SC_BLOCK_DATA) != 0);
    externalizable =
        ((flags & ObjectStreamConstants.SC_EXTERNALIZABLE) != 0);
    boolean sflag =
        ((flags & ObjectStreamConstants.SC_SERIALIZABLE) != 0);
    if (externalizable && sflag) {
      throw new InvalidClassException(
          name, "serializable and externalizable flags conflict");
    }
    serializable = externalizable || sflag;
    isEnum = ((flags & ObjectStreamConstants.SC_ENUM) != 0);
    if (isEnum && suid.longValue() != 0L) {
      throw new InvalidClassException(name,
          "enum descriptor has non-zero serialVersionUID: " + suid);
    }

    int numFields = in.readShort();
    if (isEnum && numFields != 0) {
      throw new InvalidClassException(name,
          "enum descriptor has non-zero field count: " + numFields);
    }
    fields = (numFields > 0) ?
        new ObjectStreamField[numFields] : NO_FIELDS;
    for (int i = 0; i < numFields; i++) {
      char tcode = (char) in.readByte();
      String fname = in.readUTF();
      String signature = ((tcode == 'L') || (tcode == '[')) ?
          in.readTypeString() : new String(new char[]{tcode});
      try {
        fields[i] = new ObjectStreamField(fname, signature, false);
      } catch (RuntimeException e) {
        throw (IOException) new InvalidClassException(name,
            "invalid descriptor for field " + fname).initCause(e);
      }
    }
    computeFieldOffsets();
  }

  /**
   * Writes non-proxy class descriptor information to given output stream.
   */
  void writeNonProxy(ObjectOutputStream out) throws IOException {
    out.writeUTF(name);
    out.writeLong(getSerialVersionUID());

    byte flags = 0;
    if (externalizable) {
      flags |= ObjectStreamConstants.SC_EXTERNALIZABLE;
      int protocol = out.getProtocolVersion();
      if (protocol != ObjectStreamConstants.PROTOCOL_VERSION_1) {
        flags |= ObjectStreamConstants.SC_BLOCK_DATA;
      }
    } else if (serializable) {
      flags |= ObjectStreamConstants.SC_SERIALIZABLE;
    }
    if (hasWriteObjectData) {
      flags |= ObjectStreamConstants.SC_WRITE_METHOD;
    }
    if (isEnum) {
      flags |= ObjectStreamConstants.SC_ENUM;
    }
    out.writeByte(flags);

    out.writeShort(fields.length);
    for (int i = 0; i < fields.length; i++) {
      ObjectStreamField f = fields[i];
      out.writeByte(f.getTypeCode());
      out.writeUTF(f.getName());
      if (!f.isPrimitive()) {
        out.writeTypeString(f.getTypeString());
      }
    }
  }

  /**
   * Returns ClassNotFoundException (if any) thrown while attempting to
   * resolve local class corresponding to this class descriptor.
   */
  ClassNotFoundException getResolveException() {
    return resolveEx;
  }

  /**
   * Throws an InvalidClassException if object instances referencing this
   * class descriptor should not be allowed to deserialize.  This method does
   * not apply to deserialization of enum constants.
   */
  void checkDeserialize() throws InvalidClassException {
    if (deserializeEx != null) {
      throw deserializeEx.newInvalidClassException();
    }
  }

  /**
   * Throws an InvalidClassException if objects whose class is represented by
   * this descriptor should not be allowed to serialize.  This method does
   * not apply to serialization of enum constants.
   */
  void checkSerialize() throws InvalidClassException {
    if (serializeEx != null) {
      throw serializeEx.newInvalidClassException();
    }
  }

  /**
   * Throws an InvalidClassException if objects whose class is represented by
   * this descriptor should not be permitted to use default serialization
   * (e.g., if the class declares serializable fields that do not correspond
   * to actual fields, and hence must use the GetField API).  This method
   * does not apply to deserialization of enum constants.
   */
  void checkDefaultSerialize() throws InvalidClassException {
    if (defaultSerializeEx != null) {
      throw defaultSerializeEx.newInvalidClassException();
    }
  }

  /**
   * Returns superclass descriptor.  Note that on the receiving side, the
   * superclass descriptor may be bound to a class that is not a superclass
   * of the subclass descriptor's bound class.
   */
  ObjectStreamClass getSuperDesc() {
    return superDesc;
  }

  /**
   * Returns the "local" class descriptor for the class associated with this
   * class descriptor (i.e., the result of
   * ObjectStreamClass.lookup(this.forClass())) or null if there is no class
   * associated with this descriptor.
   */
  ObjectStreamClass getLocalDesc() {
    return localDesc;
  }

  /**
   * Returns arrays of ObjectStreamFields representing the serializable
   * fields of the represented class.  If copy is true, a clone of this class
   * descriptor's field array is returned, otherwise the array itself is
   * returned.
   */
  ObjectStreamField[] getFields(boolean copy) {
    return copy ? fields.clone() : fields;
  }

  /**
   * Looks up a serializable field of the represented class by name and type.
   * A specified type of null matches all types, Object.class matches all
   * non-primitive types, and any other non-null type matches assignable
   * types only.  Returns matching field, or null if no match found.
   */
  ObjectStreamField getField(String name, Class<?> type) {
    for (int i = 0; i < fields.length; i++) {
      ObjectStreamField f = fields[i];
      if (f.getName().equals(name)) {
        if (type == null ||
            (type == Object.class && !f.isPrimitive())) {
          return f;
        }
        Class<?> ftype = f.getType();
        if (ftype != null && type.isAssignableFrom(ftype)) {
          return f;
        }
      }
    }
    return null;
  }

  /**
   * Returns true if class descriptor represents a dynamic proxy class, false
   * otherwise.
   */
  boolean isProxy() {
    return isProxy;
  }

  /**
   * Returns true if class descriptor represents an enum type, false
   * otherwise.
   */
  boolean isEnum() {
    return isEnum;
  }

  /**
   * Returns true if represented class implements Externalizable, false
   * otherwise.
   */
  boolean isExternalizable() {
    return externalizable;
  }

  /**
   * Returns true if represented class implements Serializable, false
   * otherwise.
   */
  boolean isSerializable() {
    return serializable;
  }

  /**
   * Returns true if class descriptor represents externalizable class that
   * has written its data in 1.2 (block data) format, false otherwise.
   */
  boolean hasBlockExternalData() {
    return hasBlockExternalData;
  }

  /**
   * Returns true if class descriptor represents serializable (but not
   * externalizable) class which has written its data via a custom
   * writeObject() method, false otherwise.
   */
  boolean hasWriteObjectData() {
    return hasWriteObjectData;
  }

  /**
   * Returns true if represented class is serializable/externalizable and can
   * be instantiated by the serialization runtime--i.e., if it is
   * externalizable and defines a public no-arg constructor, or if it is
   * non-externalizable and its first non-serializable superclass defines an
   * accessible no-arg constructor.  Otherwise, returns false.
   */
  boolean isInstantiable() {
    return (cons != null);
  }

  /**
   * Returns true if represented class is serializable (but not
   * externalizable) and defines a conformant writeObject method.  Otherwise,
   * returns false.
   */
  boolean hasWriteObjectMethod() {
    return (writeObjectMethod != null);
  }

  /**
   * Returns true if represented class is serializable (but not
   * externalizable) and defines a conformant readObject method.  Otherwise,
   * returns false.
   */
  boolean hasReadObjectMethod() {
    return (readObjectMethod != null);
  }

  /**
   * Returns true if represented class is serializable (but not
   * externalizable) and defines a conformant readObjectNoData method.
   * Otherwise, returns false.
   */
  boolean hasReadObjectNoDataMethod() {
    return (readObjectNoDataMethod != null);
  }

  /**
   * Returns true if represented class is serializable or externalizable and
   * defines a conformant writeReplace method.  Otherwise, returns false.
   */
  boolean hasWriteReplaceMethod() {
    return (writeReplaceMethod != null);
  }

  /**
   * Returns true if represented class is serializable or externalizable and
   * defines a conformant readResolve method.  Otherwise, returns false.
   */
  boolean hasReadResolveMethod() {
    return (readResolveMethod != null);
  }

  /**
   * Creates a new instance of the represented class.  If the class is
   * externalizable, invokes its public no-arg constructor; otherwise, if the
   * class is serializable, invokes the no-arg constructor of the first
   * non-serializable superclass.  Throws UnsupportedOperationException if
   * this class descriptor is not associated with a class, if the associated
   * class is non-serializable or if the appropriate no-arg constructor is
   * inaccessible/unavailable.
   */
  Object newInstance()
      throws InstantiationException, InvocationTargetException,
      UnsupportedOperationException {
    if (cons != null) {
      try {
        return cons.newInstance();
      } catch (IllegalAccessException ex) {
        // should not occur, as access checks have been suppressed
        throw new InternalError(ex);
      }
    } else {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * Invokes the writeObject method of the represented serializable class.
   * Throws UnsupportedOperationException if this class descriptor is not
   * associated with a class, or if the class is externalizable,
   * non-serializable or does not define writeObject.
   */
  void invokeWriteObject(Object obj, ObjectOutputStream out)
      throws IOException, UnsupportedOperationException {
    if (writeObjectMethod != null) {
      try {
        writeObjectMethod.invoke(obj, new Object[]{out});
      } catch (InvocationTargetException ex) {
        Throwable th = ex.getTargetException();
        if (th instanceof IOException) {
          throw (IOException) th;
        } else {
          throwMiscException(th);
        }
      } catch (IllegalAccessException ex) {
        // should not occur, as access checks have been suppressed
        throw new InternalError(ex);
      }
    } else {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * Invokes the readObject method of the represented serializable class.
   * Throws UnsupportedOperationException if this class descriptor is not
   * associated with a class, or if the class is externalizable,
   * non-serializable or does not define readObject.
   */
  void invokeReadObject(Object obj, ObjectInputStream in)
      throws ClassNotFoundException, IOException,
      UnsupportedOperationException {
    if (readObjectMethod != null) {
      try {
        readObjectMethod.invoke(obj, new Object[]{in});
      } catch (InvocationTargetException ex) {
        Throwable th = ex.getTargetException();
        if (th instanceof ClassNotFoundException) {
          throw (ClassNotFoundException) th;
        } else if (th instanceof IOException) {
          throw (IOException) th;
        } else {
          throwMiscException(th);
        }
      } catch (IllegalAccessException ex) {
        // should not occur, as access checks have been suppressed
        throw new InternalError(ex);
      }
    } else {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * Invokes the readObjectNoData method of the represented serializable
   * class.  Throws UnsupportedOperationException if this class descriptor is
   * not associated with a class, or if the class is externalizable,
   * non-serializable or does not define readObjectNoData.
   */
  void invokeReadObjectNoData(Object obj)
      throws IOException, UnsupportedOperationException {
    if (readObjectNoDataMethod != null) {
      try {
        readObjectNoDataMethod.invoke(obj, (Object[]) null);
      } catch (InvocationTargetException ex) {
        Throwable th = ex.getTargetException();
        if (th instanceof ObjectStreamException) {
          throw (ObjectStreamException) th;
        } else {
          throwMiscException(th);
        }
      } catch (IllegalAccessException ex) {
        // should not occur, as access checks have been suppressed
        throw new InternalError(ex);
      }
    } else {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * Invokes the writeReplace method of the represented serializable class and
   * returns the result.  Throws UnsupportedOperationException if this class
   * descriptor is not associated with a class, or if the class is
   * non-serializable or does not define writeReplace.
   */
  Object invokeWriteReplace(Object obj)
      throws IOException, UnsupportedOperationException {
    if (writeReplaceMethod != null) {
      try {
        return writeReplaceMethod.invoke(obj, (Object[]) null);
      } catch (InvocationTargetException ex) {
        Throwable th = ex.getTargetException();
        if (th instanceof ObjectStreamException) {
          throw (ObjectStreamException) th;
        } else {
          throwMiscException(th);
          throw new InternalError(th);  // never reached
        }
      } catch (IllegalAccessException ex) {
        // should not occur, as access checks have been suppressed
        throw new InternalError(ex);
      }
    } else {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * Invokes the readResolve method of the represented serializable class and
   * returns the result.  Throws UnsupportedOperationException if this class
   * descriptor is not associated with a class, or if the class is
   * non-serializable or does not define readResolve.
   */
  Object invokeReadResolve(Object obj)
      throws IOException, UnsupportedOperationException {
    if (readResolveMethod != null) {
      try {
        return readResolveMethod.invoke(obj, (Object[]) null);
      } catch (InvocationTargetException ex) {
        Throwable th = ex.getTargetException();
        if (th instanceof ObjectStreamException) {
          throw (ObjectStreamException) th;
        } else {
          throwMiscException(th);
          throw new InternalError(th);  // never reached
        }
      } catch (IllegalAccessException ex) {
        // should not occur, as access checks have been suppressed
        throw new InternalError(ex);
      }
    } else {
      throw new UnsupportedOperationException();
    }
  }

  /**
   * Class representing the portion of an object's serialized form allotted
   * to data described by a given class descriptor.  If "hasData" is false,
   * the object's serialized form does not contain data associated with the
   * class descriptor.
   */
  static class ClassDataSlot {

    /**
     * class descriptor "occupying" this slot
     */
    final ObjectStreamClass desc;
    /**
     * true if serialized form includes data for this slot's descriptor
     */
    final boolean hasData;

    ClassDataSlot(ObjectStreamClass desc, boolean hasData) {
      this.desc = desc;
      this.hasData = hasData;
    }
  }

  /**
   * Returns array of ClassDataSlot instances representing the data layout
   * (including superclass data) for serialized objects described by this
   * class descriptor.  ClassDataSlots are ordered by inheritance with those
   * containing "higher" superclasses appearing first.  The final
   * ClassDataSlot contains a reference to this descriptor.
   */
  ClassDataSlot[] getClassDataLayout() throws InvalidClassException {
    // REMIND: synchronize instead of relying on volatile?
    if (dataLayout == null) {
      dataLayout = getClassDataLayout0();
    }
    return dataLayout;
  }

  private ClassDataSlot[] getClassDataLayout0()
      throws InvalidClassException {
    ArrayList<ClassDataSlot> slots = new ArrayList<>();
    Class<?> start = cl, end = cl;

    // locate closest non-serializable superclass
    while (end != null && Serializable.class.isAssignableFrom(end)) {
      end = end.getSuperclass();
    }

    HashSet<String> oscNames = new HashSet<>(3);

    for (ObjectStreamClass d = this; d != null; d = d.superDesc) {
      if (oscNames.contains(d.name)) {
        throw new InvalidClassException("Circular reference.");
      } else {
        oscNames.add(d.name);
      }

      // search up inheritance hierarchy for class with matching name
      String searchName = (d.cl != null) ? d.cl.getName() : d.name;
      Class<?> match = null;
      for (Class<?> c = start; c != end; c = c.getSuperclass()) {
        if (searchName.equals(c.getName())) {
          match = c;
          break;
        }
      }

      // add "no data" slot for each unmatched class below match
      if (match != null) {
        for (Class<?> c = start; c != match; c = c.getSuperclass()) {
          slots.add(new ClassDataSlot(
              ObjectStreamClass.lookup(c, true), false));
        }
        start = match.getSuperclass();
      }

      // record descriptor/class pairing
      slots.add(new ClassDataSlot(d.getVariantFor(match), true));
    }

    // add "no data" slot for any leftover unmatched classes
    for (Class<?> c = start; c != end; c = c.getSuperclass()) {
      slots.add(new ClassDataSlot(
          ObjectStreamClass.lookup(c, true), false));
    }

    // order slots from superclass -> subclass
    Collections.reverse(slots);
    return slots.toArray(new ClassDataSlot[slots.size()]);
  }

  /**
   * Returns aggregate size (in bytes) of marshalled primitive field values
   * for represented class.
   */
  int getPrimDataSize() {
    return primDataSize;
  }

  /**
   * Returns number of non-primitive serializable fields of represented
   * class.
   */
  int getNumObjFields() {
    return numObjFields;
  }

  /**
   * Fetches the serializable primitive field values of object obj and
   * marshals them into byte array buf starting at offset 0.  It is the
   * responsibility of the caller to ensure that obj is of the proper type if
   * non-null.
   */
  void getPrimFieldValues(Object obj, byte[] buf) {
    fieldRefl.getPrimFieldValues(obj, buf);
  }

  /**
   * Sets the serializable primitive fields of object obj using values
   * unmarshalled from byte array buf starting at offset 0.  It is the
   * responsibility of the caller to ensure that obj is of the proper type if
   * non-null.
   */
  void setPrimFieldValues(Object obj, byte[] buf) {
    fieldRefl.setPrimFieldValues(obj, buf);
  }

  /**
   * Fetches the serializable object field values of object obj and stores
   * them in array vals starting at offset 0.  It is the responsibility of
   * the caller to ensure that obj is of the proper type if non-null.
   */
  void getObjFieldValues(Object obj, Object[] vals) {
    fieldRefl.getObjFieldValues(obj, vals);
  }

  /**
   * Sets the serializable object fields of object obj using values from
   * array vals starting at offset 0.  It is the responsibility of the caller
   * to ensure that obj is of the proper type if non-null.
   */
  void setObjFieldValues(Object obj, Object[] vals) {
    fieldRefl.setObjFieldValues(obj, vals);
  }

  /**
   * Calculates and sets serializable field offsets, as well as primitive
   * data size and object field count totals.  Throws InvalidClassException
   * if fields are illegally ordered.
   */
  private void computeFieldOffsets() throws InvalidClassException {
    primDataSize = 0;
    numObjFields = 0;
    int firstObjIndex = -1;

    for (int i = 0; i < fields.length; i++) {
      ObjectStreamField f = fields[i];
      switch (f.getTypeCode()) {
        case 'Z':
        case 'B':
          f.setOffset(primDataSize++);
          break;

        case 'C':
        case 'S':
          f.setOffset(primDataSize);
          primDataSize += 2;
          break;

        case 'I':
        case 'F':
          f.setOffset(primDataSize);
          primDataSize += 4;
          break;

        case 'J':
        case 'D':
          f.setOffset(primDataSize);
          primDataSize += 8;
          break;

        case '[':
        case 'L':
          f.setOffset(numObjFields++);
          if (firstObjIndex == -1) {
            firstObjIndex = i;
          }
          break;

        default:
          throw new InternalError();
      }
    }
    if (firstObjIndex != -1 &&
        firstObjIndex + numObjFields != fields.length) {
      throw new InvalidClassException(name, "illegal field order");
    }
  }

  /**
   * If given class is the same as the class associated with this class
   * descriptor, returns reference to this class descriptor.  Otherwise,
   * returns variant of this class descriptor bound to given class.
   */
  private ObjectStreamClass getVariantFor(Class<?> cl)
      throws InvalidClassException {
    if (this.cl == cl) {
      return this;
    }
    ObjectStreamClass desc = new ObjectStreamClass();
    if (isProxy) {
      desc.initProxy(cl, null, superDesc);
    } else {
      desc.initNonProxy(this, cl, null, superDesc);
    }
    return desc;
  }

  /**
   * Returns public no-arg constructor of given class, or null if none found.
   * Access checks are disabled on the returned constructor (if any), since
   * the defining class may still be non-public.
   */
  private static Constructor<?> getExternalizableConstructor(Class<?> cl) {
    try {
      Constructor<?> cons = cl.getDeclaredConstructor((Class<?>[]) null);
      cons.setAccessible(true);
      return ((cons.getModifiers() & Modifier.PUBLIC) != 0) ?
          cons : null;
    } catch (NoSuchMethodException ex) {
      return null;
    }
  }

  /**
   * Returns subclass-accessible no-arg constructor of first non-serializable
   * superclass, or null if none found.  Access checks are disabled on the
   * returned constructor (if any).
   */
  private static Constructor<?> getSerializableConstructor(Class<?> cl) {
    Class<?> initCl = cl;
    while (Serializable.class.isAssignableFrom(initCl)) {
      if ((initCl = initCl.getSuperclass()) == null) {
        return null;
      }
    }
    try {
      Constructor<?> cons = initCl.getDeclaredConstructor((Class<?>[]) null);
      int mods = cons.getModifiers();
      if ((mods & Modifier.PRIVATE) != 0 ||
          ((mods & (Modifier.PUBLIC | Modifier.PROTECTED)) == 0 &&
              !packageEquals(cl, initCl))) {
        return null;
      }
      cons = reflFactory.newConstructorForSerialization(cl, cons);
      cons.setAccessible(true);
      return cons;
    } catch (NoSuchMethodException ex) {
      return null;
    }
  }

  /**
   * Returns non-static, non-abstract method with given signature provided it
   * is defined by or accessible (via inheritance) by the given class, or
   * null if no match found.  Access checks are disabled on the returned
   * method (if any).
   */
  private static Method getInheritableMethod(Class<?> cl, String name,
      Class<?>[] argTypes,
      Class<?> returnType) {
    Method meth = null;
    Class<?> defCl = cl;
    while (defCl != null) {
      try {
        meth = defCl.getDeclaredMethod(name, argTypes);
        break;
      } catch (NoSuchMethodException ex) {
        defCl = defCl.getSuperclass();
      }
    }

    if ((meth == null) || (meth.getReturnType() != returnType)) {
      return null;
    }
    meth.setAccessible(true);
    int mods = meth.getModifiers();
    if ((mods & (Modifier.STATIC | Modifier.ABSTRACT)) != 0) {
      return null;
    } else if ((mods & (Modifier.PUBLIC | Modifier.PROTECTED)) != 0) {
      return meth;
    } else if ((mods & Modifier.PRIVATE) != 0) {
      return (cl == defCl) ? meth : null;
    } else {
      return packageEquals(cl, defCl) ? meth : null;
    }
  }

  /**
   * Returns non-static private method with given signature defined by given
   * class, or null if none found.  Access checks are disabled on the
   * returned method (if any).
   */
  private static Method getPrivateMethod(Class<?> cl, String name,
      Class<?>[] argTypes,
      Class<?> returnType) {
    try {
      Method meth = cl.getDeclaredMethod(name, argTypes);
      meth.setAccessible(true);
      int mods = meth.getModifiers();
      return ((meth.getReturnType() == returnType) &&
          ((mods & Modifier.STATIC) == 0) &&
          ((mods & Modifier.PRIVATE) != 0)) ? meth : null;
    } catch (NoSuchMethodException ex) {
      return null;
    }
  }

  /**
   * Returns true if classes are defined in the same runtime package, false
   * otherwise.
   */
  private static boolean packageEquals(Class<?> cl1, Class<?> cl2) {
    return (cl1.getClassLoader() == cl2.getClassLoader() &&
        getPackageName(cl1).equals(getPackageName(cl2)));
  }

  /**
   * Returns package name of given class.
   */
  private static String getPackageName(Class<?> cl) {
    String s = cl.getName();
    int i = s.lastIndexOf('[');
    if (i >= 0) {
      s = s.substring(i + 2);
    }
    i = s.lastIndexOf('.');
    return (i >= 0) ? s.substring(0, i) : "";
  }

  /**
   * Compares class names for equality, ignoring package names.  Returns true
   * if class names equal, false otherwise.
   */
  private static boolean classNamesEqual(String name1, String name2) {
    name1 = name1.substring(name1.lastIndexOf('.') + 1);
    name2 = name2.substring(name2.lastIndexOf('.') + 1);
    return name1.equals(name2);
  }

  /**
   * Returns JVM type signature for given class.
   */
  private static String getClassSignature(Class<?> cl) {
    StringBuilder sbuf = new StringBuilder();
    while (cl.isArray()) {
      sbuf.append('[');
      cl = cl.getComponentType();
    }
    if (cl.isPrimitive()) {
      if (cl == Integer.TYPE) {
        sbuf.append('I');
      } else if (cl == Byte.TYPE) {
        sbuf.append('B');
      } else if (cl == Long.TYPE) {
        sbuf.append('J');
      } else if (cl == Float.TYPE) {
        sbuf.append('F');
      } else if (cl == Double.TYPE) {
        sbuf.append('D');
      } else if (cl == Short.TYPE) {
        sbuf.append('S');
      } else if (cl == Character.TYPE) {
        sbuf.append('C');
      } else if (cl == Boolean.TYPE) {
        sbuf.append('Z');
      } else if (cl == Void.TYPE) {
        sbuf.append('V');
      } else {
        throw new InternalError();
      }
    } else {
      sbuf.append('L' + cl.getName().replace('.', '/') + ';');
    }
    return sbuf.toString();
  }

  /**
   * Returns JVM type signature for given list of parameters and return type.
   */
  private static String getMethodSignature(Class<?>[] paramTypes,
      Class<?> retType) {
    StringBuilder sbuf = new StringBuilder();
    sbuf.append('(');
    for (int i = 0; i < paramTypes.length; i++) {
      sbuf.append(getClassSignature(paramTypes[i]));
    }
    sbuf.append(')');
    sbuf.append(getClassSignature(retType));
    return sbuf.toString();
  }

  /**
   * Convenience method for throwing an exception that is either a
   * RuntimeException, Error, or of some unexpected type (in which case it is
   * wrapped inside an IOException).
   */
  private static void throwMiscException(Throwable th) throws IOException {
    if (th instanceof RuntimeException) {
      throw (RuntimeException) th;
    } else if (th instanceof Error) {
      throw (Error) th;
    } else {
      IOException ex = new IOException("unexpected exception type");
      ex.initCause(th);
      throw ex;
    }
  }

  /**
   * Returns ObjectStreamField array describing the serializable fields of
   * the given class.  Serializable fields backed by an actual field of the
   * class are represented by ObjectStreamFields with corresponding non-null
   * Field objects.  Throws InvalidClassException if the (explicitly
   * declared) serializable fields are invalid.
   */
  private static ObjectStreamField[] getSerialFields(Class<?> cl)
      throws InvalidClassException {
    ObjectStreamField[] fields;
    if (Serializable.class.isAssignableFrom(cl) &&
        !Externalizable.class.isAssignableFrom(cl) &&
        !Proxy.isProxyClass(cl) &&
        !cl.isInterface()) {
      if ((fields = getDeclaredSerialFields(cl)) == null) {
        fields = getDefaultSerialFields(cl);
      }
      Arrays.sort(fields);
    } else {
      fields = NO_FIELDS;
    }
    return fields;
  }

  /**
   * Returns serializable fields of given class as defined explicitly by a
   * "serialPersistentFields" field, or null if no appropriate
   * "serialPersistentFields" field is defined.  Serializable fields backed
   * by an actual field of the class are represented by ObjectStreamFields
   * with corresponding non-null Field objects.  For compatibility with past
   * releases, a "serialPersistentFields" field with a null value is
   * considered equivalent to not declaring "serialPersistentFields".  Throws
   * InvalidClassException if the declared serializable fields are
   * invalid--e.g., if multiple fields share the same name.
   */
  private static ObjectStreamField[] getDeclaredSerialFields(Class<?> cl)
      throws InvalidClassException {
    ObjectStreamField[] serialPersistentFields = null;
    try {
      Field f = cl.getDeclaredField("serialPersistentFields");
      int mask = Modifier.PRIVATE | Modifier.STATIC | Modifier.FINAL;
      if ((f.getModifiers() & mask) == mask) {
        f.setAccessible(true);
        serialPersistentFields = (ObjectStreamField[]) f.get(null);
      }
    } catch (Exception ex) {
    }
    if (serialPersistentFields == null) {
      return null;
    } else if (serialPersistentFields.length == 0) {
      return NO_FIELDS;
    }

    ObjectStreamField[] boundFields =
        new ObjectStreamField[serialPersistentFields.length];
    Set<String> fieldNames = new HashSet<>(serialPersistentFields.length);

    for (int i = 0; i < serialPersistentFields.length; i++) {
      ObjectStreamField spf = serialPersistentFields[i];

      String fname = spf.getName();
      if (fieldNames.contains(fname)) {
        throw new InvalidClassException(
            "multiple serializable fields named " + fname);
      }
      fieldNames.add(fname);

      try {
        Field f = cl.getDeclaredField(fname);
        if ((f.getType() == spf.getType()) &&
            ((f.getModifiers() & Modifier.STATIC) == 0)) {
          boundFields[i] =
              new ObjectStreamField(f, spf.isUnshared(), true);
        }
      } catch (NoSuchFieldException ex) {
      }
      if (boundFields[i] == null) {
        boundFields[i] = new ObjectStreamField(
            fname, spf.getType(), spf.isUnshared());
      }
    }
    return boundFields;
  }

  /**
   * Returns array of ObjectStreamFields corresponding to all non-static
   * non-transient fields declared by given class.  Each ObjectStreamField
   * contains a Field object for the field it represents.  If no default
   * serializable fields exist, NO_FIELDS is returned.
   */
  private static ObjectStreamField[] getDefaultSerialFields(Class<?> cl) {
    Field[] clFields = cl.getDeclaredFields();
    ArrayList<ObjectStreamField> list = new ArrayList<>();
    int mask = Modifier.STATIC | Modifier.TRANSIENT;

    for (int i = 0; i < clFields.length; i++) {
      if ((clFields[i].getModifiers() & mask) == 0) {
        list.add(new ObjectStreamField(clFields[i], false, true));
      }
    }
    int size = list.size();
    return (size == 0) ? NO_FIELDS :
        list.toArray(new ObjectStreamField[size]);
  }

  /**
   * Returns explicit serial version UID value declared by given class, or
   * null if none.
   */
  private static Long getDeclaredSUID(Class<?> cl) {
    try {
      Field f = cl.getDeclaredField("serialVersionUID");
      int mask = Modifier.STATIC | Modifier.FINAL;
      if ((f.getModifiers() & mask) == mask) {
        f.setAccessible(true);
        return Long.valueOf(f.getLong(null));
      }
    } catch (Exception ex) {
    }
    return null;
  }

  /**
   * Computes the default serial version UID value for the given class.
   */
  private static long computeDefaultSUID(Class<?> cl) {
    if (!Serializable.class.isAssignableFrom(cl) || Proxy.isProxyClass(cl)) {
      return 0L;
    }

    try {
      ByteArrayOutputStream bout = new ByteArrayOutputStream();
      DataOutputStream dout = new DataOutputStream(bout);

      dout.writeUTF(cl.getName());

      int classMods = cl.getModifiers() &
          (Modifier.PUBLIC | Modifier.FINAL |
              Modifier.INTERFACE | Modifier.ABSTRACT);

            /*
             * compensate for javac bug in which ABSTRACT bit was set for an
             * interface only if the interface declared methods
             */
      Method[] methods = cl.getDeclaredMethods();
      if ((classMods & Modifier.INTERFACE) != 0) {
        classMods = (methods.length > 0) ?
            (classMods | Modifier.ABSTRACT) :
            (classMods & ~Modifier.ABSTRACT);
      }
      dout.writeInt(classMods);

      if (!cl.isArray()) {
                /*
                 * compensate for change in 1.2FCS in which
                 * Class.getInterfaces() was modified to return Cloneable and
                 * Serializable for array classes.
                 */
        Class<?>[] interfaces = cl.getInterfaces();
        String[] ifaceNames = new String[interfaces.length];
        for (int i = 0; i < interfaces.length; i++) {
          ifaceNames[i] = interfaces[i].getName();
        }
        Arrays.sort(ifaceNames);
        for (int i = 0; i < ifaceNames.length; i++) {
          dout.writeUTF(ifaceNames[i]);
        }
      }

      Field[] fields = cl.getDeclaredFields();
      MemberSignature[] fieldSigs = new MemberSignature[fields.length];
      for (int i = 0; i < fields.length; i++) {
        fieldSigs[i] = new MemberSignature(fields[i]);
      }
      Arrays.sort(fieldSigs, new Comparator<MemberSignature>() {
        public int compare(MemberSignature ms1, MemberSignature ms2) {
          return ms1.name.compareTo(ms2.name);
        }
      });
      for (int i = 0; i < fieldSigs.length; i++) {
        MemberSignature sig = fieldSigs[i];
        int mods = sig.member.getModifiers() &
            (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
                Modifier.STATIC | Modifier.FINAL | Modifier.VOLATILE |
                Modifier.TRANSIENT);
        if (((mods & Modifier.PRIVATE) == 0) ||
            ((mods & (Modifier.STATIC | Modifier.TRANSIENT)) == 0)) {
          dout.writeUTF(sig.name);
          dout.writeInt(mods);
          dout.writeUTF(sig.signature);
        }
      }

      if (hasStaticInitializer(cl)) {
        dout.writeUTF("<clinit>");
        dout.writeInt(Modifier.STATIC);
        dout.writeUTF("()V");
      }

      Constructor<?>[] cons = cl.getDeclaredConstructors();
      MemberSignature[] consSigs = new MemberSignature[cons.length];
      for (int i = 0; i < cons.length; i++) {
        consSigs[i] = new MemberSignature(cons[i]);
      }
      Arrays.sort(consSigs, new Comparator<MemberSignature>() {
        public int compare(MemberSignature ms1, MemberSignature ms2) {
          return ms1.signature.compareTo(ms2.signature);
        }
      });
      for (int i = 0; i < consSigs.length; i++) {
        MemberSignature sig = consSigs[i];
        int mods = sig.member.getModifiers() &
            (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
                Modifier.STATIC | Modifier.FINAL |
                Modifier.SYNCHRONIZED | Modifier.NATIVE |
                Modifier.ABSTRACT | Modifier.STRICT);
        if ((mods & Modifier.PRIVATE) == 0) {
          dout.writeUTF("<init>");
          dout.writeInt(mods);
          dout.writeUTF(sig.signature.replace('/', '.'));
        }
      }

      MemberSignature[] methSigs = new MemberSignature[methods.length];
      for (int i = 0; i < methods.length; i++) {
        methSigs[i] = new MemberSignature(methods[i]);
      }
      Arrays.sort(methSigs, new Comparator<MemberSignature>() {
        public int compare(MemberSignature ms1, MemberSignature ms2) {
          int comp = ms1.name.compareTo(ms2.name);
          if (comp == 0) {
            comp = ms1.signature.compareTo(ms2.signature);
          }
          return comp;
        }
      });
      for (int i = 0; i < methSigs.length; i++) {
        MemberSignature sig = methSigs[i];
        int mods = sig.member.getModifiers() &
            (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
                Modifier.STATIC | Modifier.FINAL |
                Modifier.SYNCHRONIZED | Modifier.NATIVE |
                Modifier.ABSTRACT | Modifier.STRICT);
        if ((mods & Modifier.PRIVATE) == 0) {
          dout.writeUTF(sig.name);
          dout.writeInt(mods);
          dout.writeUTF(sig.signature.replace('/', '.'));
        }
      }

      dout.flush();

      MessageDigest md = MessageDigest.getInstance("SHA");
      byte[] hashBytes = md.digest(bout.toByteArray());
      long hash = 0;
      for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {
        hash = (hash << 8) | (hashBytes[i] & 0xFF);
      }
      return hash;
    } catch (IOException ex) {
      throw new InternalError(ex);
    } catch (NoSuchAlgorithmException ex) {
      throw new SecurityException(ex.getMessage());
    }
  }

  /**
   * Returns true if the given class defines a static initializer method,
   * false otherwise.
   */
  private native static boolean hasStaticInitializer(Class<?> cl);

  /**
   * Class for computing and caching field/constructor/method signatures
   * during serialVersionUID calculation.
   */
  private static class MemberSignature {

    public final Member member;
    public final String name;
    public final String signature;

    public MemberSignature(Field field) {
      member = field;
      name = field.getName();
      signature = getClassSignature(field.getType());
    }

    public MemberSignature(Constructor<?> cons) {
      member = cons;
      name = cons.getName();
      signature = getMethodSignature(
          cons.getParameterTypes(), Void.TYPE);
    }

    public MemberSignature(Method meth) {
      member = meth;
      name = meth.getName();
      signature = getMethodSignature(
          meth.getParameterTypes(), meth.getReturnType());
    }
  }

  /**
   * Class for setting and retrieving serializable field values in batch.
   */
  // REMIND: dynamically generate these?
  private static class FieldReflector {

    /**
     * handle for performing unsafe operations
     */
    private static final Unsafe unsafe = Unsafe.getUnsafe();

    /**
     * fields to operate on
     */
    private final ObjectStreamField[] fields;
    /**
     * number of primitive fields
     */
    private final int numPrimFields;
    /**
     * unsafe field keys for reading fields - may contain dupes
     */
    private final long[] readKeys;
    /**
     * unsafe fields keys for writing fields - no dupes
     */
    private final long[] writeKeys;
    /**
     * field data offsets
     */
    private final int[] offsets;
    /**
     * field type codes
     */
    private final char[] typeCodes;
    /**
     * field types
     */
    private final Class<?>[] types;

    /**
     * Constructs FieldReflector capable of setting/getting values from the
     * subset of fields whose ObjectStreamFields contain non-null
     * reflective Field objects.  ObjectStreamFields with null Fields are
     * treated as filler, for which get operations return default values
     * and set operations discard given values.
     */
    FieldReflector(ObjectStreamField[] fields) {
      this.fields = fields;
      int nfields = fields.length;
      readKeys = new long[nfields];
      writeKeys = new long[nfields];
      offsets = new int[nfields];
      typeCodes = new char[nfields];
      ArrayList<Class<?>> typeList = new ArrayList<>();
      Set<Long> usedKeys = new HashSet<>();

      for (int i = 0; i < nfields; i++) {
        ObjectStreamField f = fields[i];
        Field rf = f.getField();
        long key = (rf != null) ?
            unsafe.objectFieldOffset(rf) : Unsafe.INVALID_FIELD_OFFSET;
        readKeys[i] = key;
        writeKeys[i] = usedKeys.add(key) ?
            key : Unsafe.INVALID_FIELD_OFFSET;
        offsets[i] = f.getOffset();
        typeCodes[i] = f.getTypeCode();
        if (!f.isPrimitive()) {
          typeList.add((rf != null) ? rf.getType() : null);
        }
      }

      types = typeList.toArray(new Class<?>[typeList.size()]);
      numPrimFields = nfields - types.length;
    }

    /**
     * Returns list of ObjectStreamFields representing fields operated on
     * by this reflector.  The shared/unshared values and Field objects
     * contained by ObjectStreamFields in the list reflect their bindings
     * to locally defined serializable fields.
     */
    ObjectStreamField[] getFields() {
      return fields;
    }

    /**
     * Fetches the serializable primitive field values of object obj and
     * marshals them into byte array buf starting at offset 0.  The caller
     * is responsible for ensuring that obj is of the proper type.
     */
    void getPrimFieldValues(Object obj, byte[] buf) {
      if (obj == null) {
        throw new NullPointerException();
      }
            /* assuming checkDefaultSerialize() has been called on the class
             * descriptor this FieldReflector was obtained from, no field keys
             * in array should be equal to Unsafe.INVALID_FIELD_OFFSET.
             */
      for (int i = 0; i < numPrimFields; i++) {
        long key = readKeys[i];
        int off = offsets[i];
        switch (typeCodes[i]) {
          case 'Z':
            Bits.putBoolean(buf, off, unsafe.getBoolean(obj, key));
            break;

          case 'B':
            buf[off] = unsafe.getByte(obj, key);
            break;

          case 'C':
            Bits.putChar(buf, off, unsafe.getChar(obj, key));
            break;

          case 'S':
            Bits.putShort(buf, off, unsafe.getShort(obj, key));
            break;

          case 'I':
            Bits.putInt(buf, off, unsafe.getInt(obj, key));
            break;

          case 'F':
            Bits.putFloat(buf, off, unsafe.getFloat(obj, key));
            break;

          case 'J':
            Bits.putLong(buf, off, unsafe.getLong(obj, key));
            break;

          case 'D':
            Bits.putDouble(buf, off, unsafe.getDouble(obj, key));
            break;

          default:
            throw new InternalError();
        }
      }
    }

    /**
     * Sets the serializable primitive fields of object obj using values
     * unmarshalled from byte array buf starting at offset 0.  The caller
     * is responsible for ensuring that obj is of the proper type.
     */
    void setPrimFieldValues(Object obj, byte[] buf) {
      if (obj == null) {
        throw new NullPointerException();
      }
      for (int i = 0; i < numPrimFields; i++) {
        long key = writeKeys[i];
        if (key == Unsafe.INVALID_FIELD_OFFSET) {
          continue;           // discard value
        }
        int off = offsets[i];
        switch (typeCodes[i]) {
          case 'Z':
            unsafe.putBoolean(obj, key, Bits.getBoolean(buf, off));
            break;

          case 'B':
            unsafe.putByte(obj, key, buf[off]);
            break;

          case 'C':
            unsafe.putChar(obj, key, Bits.getChar(buf, off));
            break;

          case 'S':
            unsafe.putShort(obj, key, Bits.getShort(buf, off));
            break;

          case 'I':
            unsafe.putInt(obj, key, Bits.getInt(buf, off));
            break;

          case 'F':
            unsafe.putFloat(obj, key, Bits.getFloat(buf, off));
            break;

          case 'J':
            unsafe.putLong(obj, key, Bits.getLong(buf, off));
            break;

          case 'D':
            unsafe.putDouble(obj, key, Bits.getDouble(buf, off));
            break;

          default:
            throw new InternalError();
        }
      }
    }

    /**
     * Fetches the serializable object field values of object obj and
     * stores them in array vals starting at offset 0.  The caller is
     * responsible for ensuring that obj is of the proper type.
     */
    void getObjFieldValues(Object obj, Object[] vals) {
      if (obj == null) {
        throw new NullPointerException();
      }
            /* assuming checkDefaultSerialize() has been called on the class
             * descriptor this FieldReflector was obtained from, no field keys
             * in array should be equal to Unsafe.INVALID_FIELD_OFFSET.
             */
      for (int i = numPrimFields; i < fields.length; i++) {
        switch (typeCodes[i]) {
          case 'L':
          case '[':
            vals[offsets[i]] = unsafe.getObject(obj, readKeys[i]);
            break;

          default:
            throw new InternalError();
        }
      }
    }

    /**
     * Sets the serializable object fields of object obj using values from
     * array vals starting at offset 0.  The caller is responsible for
     * ensuring that obj is of the proper type; however, attempts to set a
     * field with a value of the wrong type will trigger an appropriate
     * ClassCastException.
     */
    void setObjFieldValues(Object obj, Object[] vals) {
      if (obj == null) {
        throw new NullPointerException();
      }
      for (int i = numPrimFields; i < fields.length; i++) {
        long key = writeKeys[i];
        if (key == Unsafe.INVALID_FIELD_OFFSET) {
          continue;           // discard value
        }
        switch (typeCodes[i]) {
          case 'L':
          case '[':
            Object val = vals[offsets[i]];
            if (val != null &&
                !types[i - numPrimFields].isInstance(val)) {
              Field f = fields[i].getField();
              throw new ClassCastException(
                  "cannot assign instance of " +
                      val.getClass().getName() + " to field " +
                      f.getDeclaringClass().getName() + "." +
                      f.getName() + " of type " +
                      f.getType().getName() + " in instance of " +
                      obj.getClass().getName());
            }
            unsafe.putObject(obj, key, val);
            break;

          default:
            throw new InternalError();
        }
      }
    }
  }

  /**
   * Matches given set of serializable fields with serializable fields
   * described by the given local class descriptor, and returns a
   * FieldReflector instance capable of setting/getting values from the
   * subset of fields that match (non-matching fields are treated as filler,
   * for which get operations return default values and set operations
   * discard given values).  Throws InvalidClassException if unresolvable
   * type conflicts exist between the two sets of fields.
   */
  private static FieldReflector getReflector(ObjectStreamField[] fields,
      ObjectStreamClass localDesc)
      throws InvalidClassException {
    // class irrelevant if no fields
    Class<?> cl = (localDesc != null && fields.length > 0) ?
        localDesc.cl : null;
    processQueue(Caches.reflectorsQueue, Caches.reflectors);
    FieldReflectorKey key = new FieldReflectorKey(cl, fields,
        Caches.reflectorsQueue);
    Reference<?> ref = Caches.reflectors.get(key);
    Object entry = null;
    if (ref != null) {
      entry = ref.get();
    }
    EntryFuture future = null;
    if (entry == null) {
      EntryFuture newEntry = new EntryFuture();
      Reference<?> newRef = new SoftReference<>(newEntry);
      do {
        if (ref != null) {
          Caches.reflectors.remove(key, ref);
        }
        ref = Caches.reflectors.putIfAbsent(key, newRef);
        if (ref != null) {
          entry = ref.get();
        }
      } while (ref != null && entry == null);
      if (entry == null) {
        future = newEntry;
      }
    }

    if (entry instanceof FieldReflector) {  // check common case first
      return (FieldReflector) entry;
    } else if (entry instanceof EntryFuture) {
      entry = ((EntryFuture) entry).get();
    } else if (entry == null) {
      try {
        entry = new FieldReflector(matchFields(fields, localDesc));
      } catch (Throwable th) {
        entry = th;
      }
      future.set(entry);
      Caches.reflectors.put(key, new SoftReference<Object>(entry));
    }

    if (entry instanceof FieldReflector) {
      return (FieldReflector) entry;
    } else if (entry instanceof InvalidClassException) {
      throw (InvalidClassException) entry;
    } else if (entry instanceof RuntimeException) {
      throw (RuntimeException) entry;
    } else if (entry instanceof Error) {
      throw (Error) entry;
    } else {
      throw new InternalError("unexpected entry: " + entry);
    }
  }

  /**
   * FieldReflector cache lookup key.  Keys are considered equal if they
   * refer to the same class and equivalent field formats.
   */
  private static class FieldReflectorKey extends WeakReference<Class<?>> {

    private final String sigs;
    private final int hash;
    private final boolean nullClass;

    FieldReflectorKey(Class<?> cl, ObjectStreamField[] fields,
        ReferenceQueue<Class<?>> queue) {
      super(cl, queue);
      nullClass = (cl == null);
      StringBuilder sbuf = new StringBuilder();
      for (int i = 0; i < fields.length; i++) {
        ObjectStreamField f = fields[i];
        sbuf.append(f.getName()).append(f.getSignature());
      }
      sigs = sbuf.toString();
      hash = System.identityHashCode(cl) + sigs.hashCode();
    }

    public int hashCode() {
      return hash;
    }

    public boolean equals(Object obj) {
      if (obj == this) {
        return true;
      }

      if (obj instanceof FieldReflectorKey) {
        FieldReflectorKey other = (FieldReflectorKey) obj;
        Class<?> referent;
        return (nullClass ? other.nullClass
            : ((referent = get()) != null) &&
                (referent == other.get())) &&
            sigs.equals(other.sigs);
      } else {
        return false;
      }
    }
  }

  /**
   * Matches given set of serializable fields with serializable fields
   * obtained from the given local class descriptor (which contain bindings
   * to reflective Field objects).  Returns list of ObjectStreamFields in
   * which each ObjectStreamField whose signature matches that of a local
   * field contains a Field object for that field; unmatched
   * ObjectStreamFields contain null Field objects.  Shared/unshared settings
   * of the returned ObjectStreamFields also reflect those of matched local
   * ObjectStreamFields.  Throws InvalidClassException if unresolvable type
   * conflicts exist between the two sets of fields.
   */
  private static ObjectStreamField[] matchFields(ObjectStreamField[] fields,
      ObjectStreamClass localDesc)
      throws InvalidClassException {
    ObjectStreamField[] localFields = (localDesc != null) ?
        localDesc.fields : NO_FIELDS;

        /*
         * Even if fields == localFields, we cannot simply return localFields
         * here.  In previous implementations of serialization,
         * ObjectStreamField.getType() returned Object.class if the
         * ObjectStreamField represented a non-primitive field and belonged to
         * a non-local class descriptor.  To preserve this (questionable)
         * behavior, the ObjectStreamField instances returned by matchFields
         * cannot report non-primitive types other than Object.class; hence
         * localFields cannot be returned directly.
         */

    ObjectStreamField[] matches = new ObjectStreamField[fields.length];
    for (int i = 0; i < fields.length; i++) {
      ObjectStreamField f = fields[i], m = null;
      for (int j = 0; j < localFields.length; j++) {
        ObjectStreamField lf = localFields[j];
        if (f.getName().equals(lf.getName())) {
          if ((f.isPrimitive() || lf.isPrimitive()) &&
              f.getTypeCode() != lf.getTypeCode()) {
            throw new InvalidClassException(localDesc.name,
                "incompatible types for field " + f.getName());
          }
          if (lf.getField() != null) {
            m = new ObjectStreamField(
                lf.getField(), lf.isUnshared(), false);
          } else {
            m = new ObjectStreamField(
                lf.getName(), lf.getSignature(), lf.isUnshared());
          }
        }
      }
      if (m == null) {
        m = new ObjectStreamField(
            f.getName(), f.getSignature(), false);
      }
      m.setOffset(f.getOffset());
      matches[i] = m;
    }
    return matches;
  }

  /**
   * Removes from the specified map any keys that have been enqueued
   * on the specified reference queue.
   */
  static void processQueue(ReferenceQueue<Class<?>> queue,
      ConcurrentMap<? extends
          WeakReference<Class<?>>, ?> map) {
    Reference<? extends Class<?>> ref;
    while ((ref = queue.poll()) != null) {
      map.remove(ref);
    }
  }

  /**
   * Weak key for Class objects.
   **/
  static class WeakClassKey extends WeakReference<Class<?>> {

    /**
     * saved value of the referent's identity hash code, to maintain
     * a consistent hash code after the referent has been cleared
     */
    private final int hash;

    /**
     * Create a new WeakClassKey to the given object, registered
     * with a queue.
     */
    WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
      super(cl, refQueue);
      hash = System.identityHashCode(cl);
    }

    /**
     * Returns the identity hash code of the original referent.
     */
    public int hashCode() {
      return hash;
    }

    /**
     * Returns true if the given object is this identical
     * WeakClassKey instance, or, if this object's referent has not
     * been cleared, if the given object is another WeakClassKey
     * instance with the identical non-null referent as this one.
     */
    public boolean equals(Object obj) {
      if (obj == this) {
        return true;
      }

      if (obj instanceof WeakClassKey) {
        Object referent = get();
        return (referent != null) &&
            (referent == ((WeakClassKey) obj).get());
      } else {
        return false;
      }
    }
  }
}
